Many different types of vacuum and pressure furnaces or ovens have been utilized by the prior art. Westeren U.S. Pat. No. 3,431,346 discloses a vacuum furnace having opposed vestibule areas communicating with a heating chamber through a transfer zone. The vestibule areas are sealed off from the heating chamber by a sealing plate which is secured to a transfer assembly, and positionable to seal off either selected vestibule area. By using the opposed vestibule areas, a part exposed to a heating cycle may be transferred to the vestibule areas for cooling without changing the operating conditions within the heating chamber.
Crain et al U.S. Pat No. 4,460,821 discloses an infrared furnace usable for firing electronic components in a non-reactive atmosphere. A product conveyor traverses the furnace, with baffle chambers surrounding the entrance and exit of the conveyor to the furnace. A seal chamber is disposed between each baffle chamber and firing chamber, with gas, such as nitrogen, under a super atmospheric pressure introduced into the baffle chambers and the seal chamber.
Pepe U.S. Pat No. 4,285,668 discloses heat treatment conveyor tunnel furnaces designed to be constructed airtight. Gas seals are formed at each end of the conveyor tunnel furnace, with gas supplied to the gas seal chamber at a pressure greater than atmospheric and greater than the gas pressure in the heating tunnel of the furnace. This difference in gas pressure prevents air from entering the furnace, and prevents any possible toxic gases in the furnace from leaking out to the atmosphere.
Bornor U.S. Pat. No. 3,447,788 is directed to an apparatus and method for heating workpieces in a furnace chamber, and then cooling the workpieces in a quenching chamber. The workpieces are introduced into the furnace chamber through a loading chamber, and are transferred from the furnace chamber to the quenching chamber through the same loading chamber. The loading chamber isolates the furnace chamber from the quenching chamber, and can be purged of oxygen and vapors from the quenching chamber during such time as it is necessary to open the furnace chamber to introduce and transfer workpieces. The admission of an oxidizing atmosphere to the furnace chamber is thus precluded, so that continuous heating of the furnace chamber may be conducted without danger of contamination.
Cope U.S. Pat. No. 2,602,653 discloses apparatus for continuously bright annealing light gauge stainless steel strips and the like. The apparatus includes a horizontal, externally heated muffle type furnace having a heating chamber therein, with baffles located at either end of the heating chamber, a cooled entry chamber ahead of the baffle at the entrance of the heating chamber, and a cooled exit chamber beyond the baffles at the exit end of the heating chamber. The strip to be annealed is continuously passed into and through the entry chamber, the heating chamber, and the cooling exit chamber. Door plates, having narrow slots through which tee strip being treated may pass, are located at the entrance end of the entry chamber. The entrance chamber, the heating chamber, and the exit chamber are maintained completely filled with a special atmosphere, such as dissociated ammonia gas, which is continuously supplied under pressure.
The Bielefeldt U.S. Pat No. 3,609,295 discloses heating apparatus for heating workpieces such as aluminum parts which are brazed together during the heating operation. Heating of the parts is conducted in the presence of a vacuum, and gas-tight doors are guided for horizontal sliding along respective tracks to separate the heating vessel from a loading vessel and an unloading vessel, and to separate the loading and unloading vessels from the atmosphere.
Barnebey U.S. Pat. No. 1,778,747 discloses a tunnel kiln for manufacturing activated charcoal. A vestibule having an inner door and an outer door is provided at each end of the tunnel kiln. The inner door moves vertically in guideways which are made gas-tight by suitable metal casings. The outer door is similarly constructed, and in order to secure a gas-tight closure for the outer door, to prevent gases from escaping or entering the tunnel kilns, a pair of wedges are arranged at the side of the door, and another pair at the lower corners. The guideways are provided with inclined abuttments for receiving these wedges, so that when the door is lowered it automatically fits itself securely against the framework.
Johanson U.S. Pat. No. 3,852,026 discloses a method for heating or heat treating material in a furnace. Goods are introduced to and removed from the furnace through lock-type feed valves provided with feed valve flaps. These flaps pivot at the upper edge thereof to permit the flaps to be swung from a closing and sealing position to an open position. A protective gas is passed to the furnace during the heating steps, and the pressure in the furnace may be maintained at a desired, substantially constant level, for instance at a gauge pressure of approximately 10 mm of water.
Crain U.S. Pat. No. 4,517,448 discloses an infrared furnace having a controlled atmosphere. The atmosphere may be nitrogen or oxygen, which is fed into the furnace under low pressure, so that the interior of the heating chamber is at a slightly higher pressure than the atmosphere surrounding the furnace. Baffle units are provided at the entrance and exit ends of the heating chamber, and utilize a series of traversely disposed baffle walls.
Other oven or kiln constructions which appear to be less relevant are described in the following U.S. patents:
______________________________________ U.S. Pat. No. Name Date ______________________________________ 1,253,487 J.L. Harper Jan. 15, 1918 1,451,815 R.W. Davenport Apr. 17, 1923 3,119,166 L. Ostermaier Jan. 28, 1964 2,992,286 N.W. Smit et al July 11, 1961 1,643,775 J. Kelleher Sept 27, 1927 2,237,966 R.P. Koehring Apr. 8, 1941 ______________________________________
DeCoriolis U.S. Pat. No. 2,033,331 discloses a heat treating furnace having a charging chamber, a discharge chamber and a middle chamber or muffle therebetween. The chambers are separated by valves. The valves include a pair of opposed flat valve seats which extend upwardly and diverging relation, and cooperate with a pair of flat valve plates which are hinged back-to-back and separately movable. Force exerted downwardly on the hinge of the valve plates wedges the plates to the valve seats.
Early U.S. Pat. No. 4,429,41 discloses a ceramic hearth door and frame, with the door slidably disposed within the frame. The back wall of the frame is tapered slightly to permit the door to lay back against the back wall for sealing engagement between the door and the recessed portion of the frame. The bottom of the door is also tapered to force the back of the door against the back of the recessed portion of the frame.
Turecek U.S. Pat. No. 4,503,784 discloses a door for an incinerator or cremator wherein a wedge-shaped opening in the incinerator or cremator is provided. The opening is wider at the top than the bottom, and tapers from the top to the bottom by straight side wall faces. The opening is of wedge-shape trapezoidal shape, and the incinerator door is of a complimentary wedge shape to the opening. The door carries a seal around its periphery, and the seal, when the door is closed, is compressed between the door and the sides and bottom of the opening. When the door is lowered in complete engagement with the opening with compression of the seal is such that the closure is rendered substantially air-tight.